This invention relates generally to high speed mail sorting equipment and deals more particularly with an improved method and apparatus for automatically controlling the speed at which envelopes are conveyed in the magazine section of a mail sorting machine.
In order to efficiently sort the large volumes of mail that are sent and received each day by various businesses, institutions, governmental units and other entitles that handle large amounts of mail, various types of mail sorting machines have been proposed. One type of high speed mail sorter that has been successful is shown in by U.S. Pat. No. 4,275,875 which issued to Roy Akers on June 30, 1981 and which is owned by the assignee of the present application. In this type of machine, the envelopes which are to be sorted are loaded on a magazine section of the machine with the envelopes situated side to side on edge. An envelope feeding mechanism delivers the envelope supply to a pickoff station at which the envelopes are picked off one at a time from the envelope supply by vacuum belts or another type of pickoff device. The envelopes are thereafter handled individually, and each envelope is conveyed past a reading station at which its zip code or another code imprinted on the envelope is read, either by a human operator or by a code reading device. Envelopes which have the same or a similar code are thereafter directed into the same storage bins by the mail sorting equipment.
Although this type of machine has been favorably received and has performed well for the most part, it has not been wholly free of problems. One of the most difficult problems has been to assure that the envelopes are repeatedly picked off one at a time from the envelope supply in the magazine section of the machine. In order for the vacuum belts to properly separate the individual envelopes from the envelope supply, the feeding system must be able to accommodate different types, sizes and thicknesses of envelopes. For example, if relatively thin envelopes are being sorted, there is a tendency for the envelopes to bunch tightly together and thus adhere to one another at the pickoff station. This tightly bunched condition of the envelopes often results in double picking and other mispicking problems. Conversely, if the envelopes are not held together tightly enough, as tends to occur when thick envelopes are being handled, similar picking problems arise and the through put of the machine also suffers.
Various types of envelope feeding mechanisms have been proposed for delivery of the envelopes to the pickoff device, including chains, augers, belts, push blocks and other conveyor systems. In order to permit the feeding mechanism to accommodate different mail thicknesses, a speed control knob has been provided so that the operator can slow the envelope feeder down when handling thin envelopes and speed it up when handling thicker mail. However, it is necessary for the human operator of the machine to closely observe the feeding operation and to manually adjust the speed control knob according to the mail that is being handled at each particular time. Due to human error and inattention, it is common for the control knob to be ignored so that the feeding mechanism generally operates at a constant speed even when the mail thickness changes. Consequently, this type of arrangement does not eliminate the double picking problems and other inefficiencies previously mentioned.